Dakki

This is defo the kind of BL that I avoid, but I can think of a few off the top of my head!
Paper Flower https://www.mangago.zone/read-manga/paper_flower/
which is a webtoon adapted from the short novel of the same name, the novel raw is at https://booktoki307.com/novel/6808874 (you can use the Chrome extension called DeepL Translate to translate the raws to your preferred language from the orig Korean, which is better at translating than Google, but there's not English translation out yet)
The ML is a completely asinine mofo jerk to the MC almost the entire duration of the story in the novel. Expect him to physically and sexually assault to MC all the fucking time and also gaslight him...poor kid.
A good BL novel (doesn't currently have manhua adaptation but may in the future) called Transmigrated as the Cannon Fodder Abandoned by the Movie Star https://www.novelupdates.com/series/transmigrated-as-the-cannon-fodder-abandoned-by-the-movie-star/ is about a guy who is the most unfortunate victim of transmigration I know except the MC in Soul of Negary https://www.novelupdates.com/series/soul-of-negary/ (not a BL). When MC transmigrates, he is forced into complete social isolation by the mofo system, and can only contact the phone of his husband via text message. Due to the limitations of the plot, his husband never reads these messages until a long time later during the crematorium chasing plot. But because the only person in the world who could acknowledge his existence for years refused to answer his desperate messages which begged for even the slightest bit of attention, the MC developed an extreme case of suicidal ideation, depression, an inability to accept the affection of others, and an ingrained/habitual desire for self harm as a means to calm his turbulent emotions. But the mofo asshole ML and he still get together and stay together despite the fact that ML was the one responsible for MC's illness and deep unhappiness. I wanted to shoot the ML and author multiple times during reading that book! And hug the MC! But the author probably has already received so many knives in the mailbox by other readers that I didn't send any...lol
There are a lot of shitty toxic BL romance in novels I've read, so I won't list more...but the writing in that one I described in pretty top notch.
Other notable BL with toxic couples:
https://www.mangago.zone/read-manga/drunk_in_love/ (this is a adapted from the novel https://www.novelupdates.com/series/years-of-intoxication/ and the ML is the biggest mofo of all time I swear, the author Shui Qian Cheng/水千丞 is fond of the toxic love trope, the popular books Professional Body Double and Beloved Enemy both feature asshole toxic semes, Beloved Enemy also has a censored cdrama adaptation)
https://www.mangago.zone/read-manga/jinx/
https://www.mangago.zone/read-manga/kiss_me_liar/ (omegaverse adapted from Korean novel of the same name https://www.novelupdates.com/series/kiss-me-liar/)
https://www.mangago.zone/read-manga/yahwacheop/
https://www.mangago.zone/read-manga/bj_alex/ (one of my personal fave webtoons)
https://www.mangago.zone/read-manga/black_lotus/
And even more can be found in a list like this: https://www.mangago.zone/home/mangalist/1038032/
or you can search on your own at https://www.mangago.zone/tag/toxic%20seme/ or just search a similar tag you're interested in
If you have more interest in danmei novels of this type that don't have manhua adaptations yet, send me a message or just ask here, but keep in mind this question area on mangago is monitored by admin so that it stays in line with the theme of questions related to manga, so it would be better to send dm

Here's a list: https://www.mangago.zone/home/mangalist/1311275/

Thank you!! Yeah, I usually avoid red flags especially in BLs but i’m currently down a rabbit hole in search of something!!